GB2108730A

GB2108730A - Power control unit

Info

Publication number: GB2108730A
Application number: GB08224515A
Authority: GB
Inventors: Yoshiaki Nishida; Takeshi Honjo
Original assignee: Canon Inc; Copyer Co Ltd
Current assignee: Canon Inc; Canon Finetech Nisca Inc
Priority date: 1981-09-01
Filing date: 1982-08-26
Publication date: 1983-05-18
Also published as: JPS5838972A; DE3232505A1; DE3232505C2; GB2108730B

Abstract

A power control unit for controlling the power to a fixer or a document exposure lamp 18 of a copying machine has a digital processor receiving a serial pulse signal C from zero crossing detector 8 and produces a phase angle control signal D based on the serial pulse signal. The energization of a load is controlled by triac 16 which is controlled by the control pulse signal D. <IMAGE>

Description

SPECIFICATION Power control unit Background of the invention Field of the invention The present invention relates to a power control unit for a copying machine or the like.

Description of the prior art Prior art power control unit for the copying machine or the like for controlling a power to a document exposure lamp or a fixer includes a phase control circuit which is an analog circuit using capacitor devices. In such an analog circuit which uses the capacitor devices, a circuit configuration is complex and a cost is expensive.

As temperature control units for the fixer of the copying machine, a proportional control unit and an integration control unit have been known. The proportional control method controls a temperature of the fixer to a desired temperature (preset temperature) based on a value proportional to a difference between the preset temperature and a measured temperature of the fixer. The integration control method controls the temperature of the fixer based on the integration of a difference between the preset temperature and the fixture temperature.

Fig. 1 shows a schematic diagram of the temperature control for the fixer by the integration control method, and Fig. 2 shows a schematic diagram of the temperature control for the fixer by the proportional control method. In Figs. 1 and 2, T,denotes a preset temperature of the fixer, and a heater of the fixer is energized at a time A. In the integration control method of Fig. 1, an overshoot occurs immediately after a time B at which the fixer temperature fist reaches the preset temperature T,, and a substantial time is required for the fixer temperature to converge to the preset temperature. Because of such overshoot, parts of the fixer may be degraded or broken. On the other hand, the integration control method has an advantage of high stability to the absorption of heat from the fixer by a transfer paper.In the proportional control method shown in Fig. 2, no overshot occurs unlike the integration control method. However, it has a problem that a control center temperature (or preset temperature To) falls by the absorption of heat by the transfer paper fed into the fixer.

In one aspect the present invention aims to provide a power control unit for a copying machine or the like capable of exact power control with a low cost.

In another aspect the present invention aims to provide a power control unit capable of controlling a load power by a digital signal.

In a further aspect the present invention aims to provide a power control unit capable of controlling the load power in a copying machine or the like.

In yet another aspect the present invention aims to provide a digital controller which forms control signals in a form advantageous to control a copying machine which uses a computer.

In a still further aspect the present invention aims to provide a temperature control unit for a fixer which allows the fixer temperature to rapidly reach a preset temperature after the start of heating of the fixer and which can maintain the fixer temperature stably after the fixer temperature has reached the preset temperature.

It is a further object of the present invention to provide a temperature control unit for a fixer which prevents the fall of a preset temperature due to the absorption of heat of the fixer by a transfer paper.

Fig. 1 shows a temperature change of a fixer in a prior art integration control method; Fig. 2 shows a temperature change of a fixer in a prior art proportional control method; Fig. 3 shows a circuit diagram of one embodiment in accordance with a control method of the present invention; Figs. 4 and 5 show waveforms for explaining the operation of Fig. 3; Figs. 6 and 7 show waveforms for explaining the operations in the integration control method and the proportional control method, respectively; Fig. 8 shows a temperature change of a fixer in one embodiment of the present invention; Figs. 9 and 10 show flow charts for effecting the temperature control shown in Fig. 8; and Fig. 11 shows a temperature change of a fixer in accordance with another embodiment of the present invention.

Detailed description of the preferred embodiment The preferred embodiments of the present invention are explained below with reference to Figs. 3-11. Fig. 3 shows a circuit diagram of a power control unit of the present invention. In the present embodiment, a well-known one-chip CPU (hereinafter referred to a microcomputer or MPU) 12 containing an analog-to-digital converter is used to simplify the overall circuit configuration. A zero-crossing detector 8 comprises a transformer 2, a full-wave rectifier having four diodes and a transistor 6. Input terminals of the zero-crossing detector 8 are connected to an A.C. power supply (commercial line) 10 and an output terminal is connected to an interrupt (INT) port of the MPU 12. Fig. 4A-C show signal waveforms at points A-C shown in Fig. 3.Fig. 4A shows a sinusoidal waveform before the full-wave rectification, Fig.

48 shows a waveform after the full-wave rectification and Fig. 4C shows a waveform at a collector of the transistor 6. The waveform C is generated in synchronism with a zero-crossing point of the input waveform. The function of the zero-crossing detector 8 is well known in the art and hence it is not explained here. The MPU 12 is interrupted when the pulse applied to the terminal INT falls from a high level to a low level and executes the interrupt processing with higher priority than other controls. After the interrupt processing, the MPU 12 immediately returns to the processing before the interrupt.

An output port P of the MPU 12 is connected to a gate of a TRIAC 16 through a pulse transformer 14. The TRIAC 16 is turned on and off by the signal from the output port P to control the energization of a fixer heater 1 8. Numeral 20 denotes an A.C. power supply (commercial line) and numeral 22 denotes a current limiting reactor. Output ports SOSn of the MPU 12 are connected to gate control terminals of analog gates G0-G , respectively.Gate signals are supplied in accordance with a control program to open the analog gates G0rGn.An output terminal of the analog gates Go as well as the output terminals of other analog gates Ci 1-G are connected to an analog-to-digital conversion (ADC) input port of the MPU 12 and an input terminal of the analog gate Go is connected to an output terminal of an amplifier 24. An input terminal of the amplifier 24 is connected to a temperature sensing element (e.g. thermistor) 26 for the fixer.Input terminals of other analog gates GGn are connected to various detection means and other output ports L0-L3 and M0-M2 of the MPU 12 are connected to a digital-to-analog converter or a control circuit although they are not explained here because they are not pertinent to the present invention.

A signal from the temperature sensing thermistor 26 for the fixer is amplified by the amplifier 24, the output of which is applied to the input terminal of the analog gate G,. The analog gate Go is opened by the gate control signal from the output port SO of the MPU 12 to gate the signal from the amplifier 24 to the ADC input port of the MPU 12. The MPU 12 converts the input analog signal to a digital signal to produce the control signal for controlling the turn-on and turn off of the TRIAC 1 6 at the output port P.

Referring now to Fig. 5, an ON timing for the conduction angle control for the TRIAC 16 is explained. A waveform C in Fig. 5 is identical to the pulse (Fig. 4C) applied to the INT port of the MPU 1 2 and it is in synchronism with the zerocrossing point of the A.C. power supply 10, as described above. A waveform D of Fig. 5 shows a pulse produced at the output port P. The TRIAC 1 6 is turned on by the pulse D. The ON-state of the TRIAC 16 is maintained until the next zerocrossing point of the output current of the A.C.

power supply 20 (which is normally identical to the A.C. power supply 10). Fig. 5E shows a waveform of a current flowing in the fixer heater 1 8. The amount of energization of the fixer heater 1 8 is controlled by varying a time period t from the zero-crossing point to the time point at which the pulse D is produced.

Fig. 6 shows a flow chart for controlling the temperature of the fixer by the integration control method. In a step 30, it is checked if a sampling cycle timer for allowing to read the signal from the thermistor 26 into the MPU 12 has counted a predetermined time period, and if the decision is YES (that is, time-up), the process goes to a step 32. A sampling cycle is selected to be lower than one half of the frequency of temperature change.

In the step 32, the MPU 12 selects the output port SO to supply the gate control signal to the analog gate Go to read the analog output of the amplifier 24 into the input port ADC. In a step 34, the analog output read into the input port ADC is converted to the digital signal by the analog-todigital converter in the MPU 12. The converted digital signal is designated by Tsn In a step 36, a preset reference value Tb is substracted from Tsn to produce a difference ATn. (åTn=TsnTb). In a step 38, an appropriate constant a is multiplied by ATn to produce a product Sn. (Sn=aATn). In a step 40, n In n=1 is calculated.In a step 42, a sign of In is checked, and if it is negative, the process goes to a step 44 where In is substituted by zero and, in a step 46, the value of In is stored in a memory in the MPU 12. If In is positive, the process goes directly to the step 46 and then goes back to the step 30. On the other hand, as descrribed above, the MPU 12 starts the interrupt processing when the pulse applied to the port INT of the MPU 12 changes from the high level to the low level and sets a time interval proportional to the value of In stored in the memory into a timing generation timer which determines an ON timing of the TRIAC 16.

In the step 30, if the sampling cycle timer has not yet counted the predetermined time period, it is checked in a step 48 if the TRIAC ON-timing t has been set in the timing generation timer, and if the decision is NO the process goes back to the step 30, and if the decision is YES, the process goes to a step 50. In the step 50, if the timing generation timer has not yet counted the predetermined time period t, the process goes back to the step 30, and if it has counted the predetermined time period t, the process goes to a step 52 where the MPU 12 produces the pulse D at the output port P to turn on the TRIAC 16.In a step 54, it is checked if a firing pulse (TRIAC turn-on pulse) output timer which starts counting simultaneously with the pulse D from the output port P has counted a predetermined count, and if the decision is NO, the process goes back to the step 52, and if the decision is YES, the process goes to a step 56 where the timing generation timer and the firing pulse output timer are reset and the process goes back to the step 30.

Fig. 7 shows a flow chart for controlling the temperature of the fixer by the proportional control method. Steps 60, 62, 64 and 66 of Fig. 7 are similar to the steps 30, 32, 34 and 36 of Fig. 6, and steps 72-80 of Fig. 7 are similar to the steps 48-56 of Fig. 6. Accordingly, those steps are not explained here and steps 68 and 70 unique to Fig. 7 are explained.In the step 68, Cn=ATn+Y is calculated, and in the step 70, Cn is stored in the memory, where p and a are positive constants selected to meet a relation of Cn=,ssåTn+y~O for various values of ATn. As explained before in conjunction with Fig. 6, the MPU 12 starts the interrupt processing when the pulse applied to the port INT of the MPU 12 changes from the high level to the low level and sets a time interval proportional to Cn derived in the step 68 and stored in the memory into the timing generation timer which determines the TRIAC ON-timing.

Fig. 8 shows a temperature change of the fixer when the temperature of the fixer is controlled by a combination of the proportional control method and the integration control method. As seen from Fig. 8, the proportional control method is used from the start of heating of the fixer (time A) to the time B when the fixer temperature reaches the preset temperature To and the integration control is used after the time B to control the fixer temperature. As a result, the overshoot encountered in the prior art is prevented and stable control is attained to the absorption of heat by the transfer paper during the copying operation.

A flow chart for effecting the temperature control of Fig. 8 is shown in Figs. 9 and 10.

Steps 60, 62, 64, 68, 70, 72, 74, 76, 78 and 80 of Fig. 9 are similar to those in the flow chart of Fig. 7 and hence they are not explained here.

Steps 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54 and 56 are similar to those in the flow chart of Fig. 6 and hence they are not explained here.

In a step 82 of Fig. 9 (proportional control), it is checked if Tsn has reached a preset second reference value Tb (corresponding to the preset value To in Fig. 8). If the decision is NO, the process goes to the step 66, where a preset first reference value Tb' is subtracted from Tsn to produce a difference AT. The subsequent steps are identical to those shown in Fig. 7.

In the step 82, if the decision is YES, the process jumps toQa in the flow chart of Fig. 10.

Then, as the same steps as the flow chart of Fig.

6, that is, the integration control steps are carried out. The first reference value Tb' is smaller than the second reference value Tb which is selected to prevent the overshoot when the temperature control for the fixer changes from the proportional control to the integration control.

Fig. 11 shows a temperature change of the fixer when another control method is used. in Fig.

11, a temperature T1 lower than the preset temperature To of the fixer is additionally set, and the fixer is continuously heated from the start of heating of the fixer (time A) to a time C when the fixer temperature reaches the temperature T1, and the fixer temperature is controlled by the integration control method after the fixer temperature has reached the temperature T1. In this case, as seen from Fig. 11, the overshoot of the fixer temperature is small and it can be suppressed below a value which may cause the degradation of the fixer. According to the control shown in Fig. 11, the time from the start of heating to the time when the fixer temperature reaches the preset temperature To is reduced.The control shown in Fig. 11 is attained by periodically reading the signal from the thermistor 26 into the MPU 1 2 and carrying out the steps of the flow chart of Fig. 6 (integration control) after the signal from the thermistor 26 has reached a value corresponding to the temperature T1.

As described above, according to the present embodiments, the load power of the fixer in the copying machine can be exactly phase-controlled by using the computer. According to the present embodiments, the overshoot which would usually occur when the fixer temperature reaches the preset temperature after the start of heating is prevented while maintaining the stability to the absorption of heat from the fixer by the transfer paper. The present embodiments accomplish the combined control of the proportional control and the integration control, and the combined control of the continuous heating and the integration control by the very simple circuit configuration by using the microcomputer. A recent trend is to control the operation of the copying machine by the microcomputer. The present invention can be embodied by merely adding simple hardware circuits to the microcomputer. In addition, since the serial pulses synchronized with the power supply are supplied to the microcomputer to form the control signals, a sequence timing control can be attained.

It should be understood that the present invention is applicable not only to the temperature control of the fixer but also to control the load power of the copying machine such as the power of the document exposure lamp.

It should also be understood that the present invention is not limited to the embodiments described above but various modifications can be made within a scope of the appended claim.

Claims

1. A power control unit comprising: means for generating a serial pulse signal; a digital processor responsive to said serial pulse signals for producing a phase angle control pulse signal based on said serial pulse signal; and switching means for controlling the energization of a load in accordance with said control pulse signal.

2. A power control unit according to Claim 1 further comprising detection means for detecting a status of said load to determine a timing to generate said control pulse signal.

3. A power control unit according to Claim 2 wherein said means for generating the serial pulse signal includes zero-crossing detection means for detecting a zero-crossing point of an A.C. signal.

4. A power control unit according to Claim 3 wherein said switching means is a TRIAC triggered by said pulse control signal.

5. A digital control unit comprising: means for rectifying a signal from a power supply; means responsive to an output of said rectifying means for produce a serial pulse synchronized with said power supply; and a computer responsive to said serial pulse to produce a control signal based on said serial pulse.

6. A digital control unit according to Claim 5 wherein said serial pulse is supplied to an interrupt port of said computer.

7. A power control unit comprising: first means for generating a control pulse under a proportional control; second means for generating a control pulse under an integration control; and switching means for controlling the energization of a load by the control pulse of either said first means or said second means.

8. A power control unit substantially as hereinbefore described with reference to any of Figures 3 to 11 of the accompanying drawings.